Printer sheet vacuum transport curled sheets acquisition

ABSTRACT

The transporting of flimsy print media sheets having curled sheet edges being fed from a fuser or other input onto a vacuum sheet transport belt system is provided with improved acquisition by simultaneously blowing the upper surface of the sheet&#39;s curled lead edge area down towards the vacuum belt transport with a positive pressure airflow while the vacuum sheet transport is attracting the sheet with its an underlying vacuum manifold airflow. Both the vacuum manifold airflow and the positive pressure airflow may be respectively provided solely by the air intake and the air exhaust from a single blower. The positive pressure airflow may be provided from a manifold extending transversely over at least the upstream end of the vacuum belt transport, spaced therefrom, and feeding air to one or more air jets.

[0001] Vacuum belt sheet transports are desirable for certain paper paths of various xerographic printers and other sheet transporting applications, especially in high speed printers. For example, for providing the downstream sheet transport away from an upstream fuser roll nip in which the xerographic toner images are thermally fused onto the printed sheets. However, as is also well-known, such print media sheets are typically relatively flimsy, and may have tendencies to curl, due to ambient moisture, fusing, and other factors. Where a print media sheet is fed out of a fuser or other upstream transport with a lead edge curl, the sheet lead edge may be curled away from the downstream surface of the vacuum belt transport system. This can interfere with the vacuum acquisition and hold-down of the sheet leading edge portion by the vacuum belt transport system, and thus can even cause sheet jams and/or slippage of the sheet relative to the sheet transport. Large area color printing presents particularly difficult problems with sheet curling tendencies, especially for duplex printing. Sheets with an upwardly curled lead edge, especially if moving at a high enough process speed (for example, in 120 or more pages per minute printers), may be further lifted above the desired sheet feeding path by bluff body forces and potentially “airplaning,” that is, aerodynamically lifting due to the media assuming a wing shape.

[0002] It will be appreciated by those skilled in the art that vacuum belt sheet transport systems, and their typical fan blower systems providing vacuums to vacuum plenums underlying the transport belt(s), are well-known and need not be described in detail herein. Some examples of vacuum belt transport systems are disclosed in Xerox Corporation U.S. Pat. No. 4,294,540 issued Oct. 13, 1981; U.S. Pat. No. 4,618,138 issued Oct. 21, 1986; U.S. Pat. No. 4,825,255 issued Apr. 25, 1989; U.S. Pat. No. 4,831,419 issued May 16,1989; and U.S. Pat. No. 4,921,240 issued May 1,1990.

[0003] Disclosed in the embodiment herein is a very low cost system for helping to overcome this problem, in which the exhaust or pressure side of the existing vacuum blower or other vacuum source for the vacuum transport system may be utilized to provide a downward air jet system acting on an upwardly curled sheet lead edge area to blow the sheet down towards the vacuum transport belt system in cooperation with its existing vacuum attraction system. Thereby the curled sheet may be acquired earlier and/or more effectively for further downstream transporting of the sheet on the vacuum sheet transport system.

[0004] That is, as disclosed in the embodiment herein, the normally vented exhaust of a vacuum blower system may be utilized to create a positive pneumatic force above the curled sheet to force the curled sheet down closer to the vacuum plenum of the vacuum sheet transport belt system for improved sheet acquisition thereby. However, it will be appreciated that, although more costly, two separate blowers could be provided for the dual airflows system disclosed herein, providing an independent positive air pressure source.

[0005] Although a post-fuser vacuum transport system utilization is illustrated here, the present system may be utilized in various other sheet transport applications. For example, to overcome the tendency of the trailing edge of a sheet to flip up as it goes into a roll pressure fuser in which the outer edges of the sheet are pulled into the fuser nip slightly faster than the center of the sheet. In a post-fuser vacuum transport system the disclosed embodiment can provide enhanced air flow against the sheet which can provide additional advantages of enhanced or faster cooling and moisture dissipation of the heated sheets exiting a typical xerographic thermal toner image fuser of a xerographic printer.

[0006] It has been found that the positive pressure and downward force on the top surface of a curled sheet from an impinging flow of positive air pressure air jets from the vacuum blower exhaust source, or other source, can be initially much larger than the downward force on that same curled sheet edge bottom surface from the airflow from the vacuum plenum of the underlying vacuum transport. This curled sheet acquisition or control system efficiency improvement can also further enhance sheet transport when the sheet is too narrow or small to fully cover enough of the vacuum ports of the vacuum plenum of the vacuum sheet transport system.

[0007] With no significant increase in cost (only minor thin wall plastic or metal ducting additions), with no extra blower motors required, and with no increase in power requirements (even a possible power reduction), the combination of positive air pressure force applied on the top of the sheet and negative air pressure applied from underneath the sheet can increase the total sheet downward or normal force, and therefore improve the sheet forward feeding force with reduced slippage of the sheet relative to its vacuum belt sheet transport system. The total flow for both sheet acquisition and sheet traction is more efficient.

[0008] Even with or after sheet acquisition, significant vacuum transport air leakage flow may exist, affecting transport of acquired sheets, especially for smaller media sizes which leave many of the vacuum ports uncovered by the media. Also, media with edges that curl downwardly towards the transport belt(s) may appear to be acquired but may not be sufficiently. The augmenting positive airflow from above can further flatten such sheets down against the vacuum transport and thus minimize its potential for slippage.

[0009] In the Figures of the embodiment a pressure plenum and air jets are illustrated as overlying only the upstream or sheet input end of the vacuum sheet transport system, for maximum effect on the entering sheet's leading area. However, optionally, additional positive downward airflow and air pressure may be similarly applied for a further downstream distance overlying much more of the vacuum sheet transport system to enhance the normal force of the paper against the transport belts from a combination of the underlying vacuum and the overlying air pressure over a much larger area.

[0010] It will be appreciated by those skilled in the art that it is known in the art to use, in sheet-separator-feeders, which have vacuum corrugating sheet feed heads, the exhaust from the vacuum blower for angled air knives assisting the lifting and separation of sheets in a stack of sheets in the sheet feeder to be acquired and fed by the sheet feed head. Such sheet-separator air knives may blow laterally toward the side or front edge of the stack of sheets for sheet separation before acquisition. For example, U.S. Pat. No. 6,186,492 issued Feb. 13, 2001 to Dechau, et al; U.S. Pat. No. 6,264,188 issued Jul. 24, 2001 to Taylor, et al; and U.S. Pat. No. 6,352,255 issued Mar. 5, 2002 to Taylor.

[0011] A specific feature of the specific embodiment disclosed herein is to provide a sheet transport system with a sheet feeding path for transporting flimsy print media sheets having upper and lower surfaces, at lease some of which flimsy print media sheets in said sheet transport system are curled, said sheet transport system including at least one vacuum sheet transport system and at least one non-vacuum sheet transport system; wherein said vacuum sheet transport system has a vacuum blower providing a vacuum airflow to said vacuum sheet transport system for providing vacuum attraction of the lower surface of said sheets against said vacuum sheet transport system, and wherein said vacuum blower has a positive air pressure exhaust airflow output corresponding to said vacuum airflow; wherein a positive air pressure airflow system is provided and positioned to direct positive pressure air flow against at least a portion of the upper surface of said flimsy print media sheets being fed in said sheet transport system to blow said curled towards said sheet feeding path.

[0012] Further specific features disclosed in the embodiment herein, individually or in combination, include those wherein rein said positive air pressure airflow system providing a positive air pressure against said flimsy print media sheets is provided by said exhaust airflow output of said vacuum blower; and/or wherein said non-vacuum sheet transport system is a fuser imparting curl to at least some of said flimsy print media sheets, which curled print media sheets are being fed towards said vacuum sheet transport system, and wherein said positive air pressure airflow system providing a positive air pressure against said flimsy print media sheets is blowing said sheets towards said vacuum sheet transport system to assist in the engagement of said curled print media sheets by said vacuum sheet transport system; and/or wherein said positive air pressure airflow system includes a positive air pressure manifold extending transversely over at least one end of said vacuum sheet transport system, spaced therefrom and feeding positive air pressure air to one or more air jets providing positive pressure air flow towards at least the leading edge area of said flimsy print media sheets being fed onto said vacuum sheet transport system; and/or a sheet transport system with a sheet feeding path for transporting flimsy print media sheets having a tendency for curled sheet edges downstream in said sheet feeding path, said sheet transport system including a downstream pneumatic vacuum sheet transport system and an upstream non-vacuum sheet transport system feeding said curled edge sheets onto said downstream pneumatic vacuum sheet transport system; wherein said downstream pneumatic vacuum sheet transport system has a pneumatic vacuum source with a vacuum airflow input to said downstream pneumatic vacuum sheet transport system for providing vacuum attraction of said sheets against said downstream pneumatic vacuum sheet transport system, and wherein said pneumatic vacuum source has a positive air pressure exhaust airflow output system corresponding to said vacuum airflow input, and wherein said positive air pressure exhaust airflow output system is positioned to direct positive pressure air flow towards at least the upstream edge of said downstream pneumatic vacuum sheet transport system and towards a curled sheet edge being fed onto said downstream pneumatic vacuum sheet transport system by said upstream non-vacuum sheet transport system, to blow said curled sheet edge towards vacuum engagement with said downstream pneumatic vacuum sheet transport system; and/or wherein said upstream non-vacuum sheet transport system is a xerographic thermal roll fuser imparting curl to said flimsy print media sheets; and/or a method of transporting flimsy print media sheets having curled sheet edges comprising feeding said curled sheets out over a vacuum sheet transport belt system and attracting the sheet there towards with an underlying vacuum manifold airflow and simultaneously blowing the upper surface of the sheet down towards said vacuum belt transport with a positive pressure airflow, wherein both said vacuum manifold airflow and said positive pressure airflow applied to the upper surface of the sheet are respectively provided solely by the air intake and the air exhaust from a single air blower; and/or wherein said positive pressure airflow is provided from a positive air pressure manifold extending transversely over at least the upstream end of said vacuum sheet transport belt system, spaced therefrom, which positive air pressure manifold is feeding air to one or more air jets providing said positive pressure air flow towards at least the curled sheet edge being fed out over said vacuum sheet transport belt system.

[0013] The term “reproduction apparatus” or “printer” as used herein broadly encompasses various printers, copiers or multifunction machines or systems, xerographic or otherwise, unless otherwise defined in a claim. The term “sheet” herein refers to a usually flimsy physical sheet of paper, plastic, or other suitable physical substrate for images, whether precut or web fed.

[0014] As to specific components of the subject apparatus or method, or alternatives therefor, it will be appreciated that, as is normally the case, some such components are known per se in other apparatus or applications, which may be additionally or alternatively used herein, including those from art cited herein. For example, it will be appreciated by respective engineers and others that many of the particular component mountings, component actuation's, or component drive systems illustrated herein are merely exemplary, and that the same novel motions and functions can be provided by many other known or readily available alternatives. All cited references, and their references, are incorporated by reference herein where appropriate for teachings of additional or alternative details, features, and/or technical background. What is well known to those skilled in the art need not be described herein.

[0015] Various of the above-mentioned and further features and advantages will be apparent to those skilled in the art from the specific apparatus and its operation or methods described in the example below, and the claims. Thus, the present invention will be better understood from this description of this specific embodiment, including the drawing figures (which are approximately to scale, except that the vacuum belt sheet transport would typically be longer than as illustrated here) wherein:

[0016]FIG. 1 is a partially schematic side view of an improved sheet acquisition and transport system, as one example of the subject system; and

[0017]FIG. 2 is a top view of the system of FIG. 1.

[0018] Referring in more detail to the exemplary sheet acquisition and transport system 10 of FIGS. 1 and 2, only those relevant portions of an otherwise conventional exemplary xerographic printer need be illustrated. In particular, a conventional xerographic roll fuser 12 is sequentially feeding out printed and fused sheets 14, at least some of which sheets 14 will have an upward lead edge curl, as illustrated. This upward lead edge curl of the sheet 14 can interfere with the desired acquisition of that sheet 14 down onto the moving transport belts 22 of a conventional vacuum sheet transport system 16 downstream of the fuser 12 by lifting that area of the sheet 14 up away from that transport system 16. The vacuum sheet transport system 16 has a conventional underlying apertured vacuum plenum 18 connected by a conventional negative pressure manifold to the suction side or input of a conventional vacuum blower 30. The vacuum sheet transport system 16 may be of variable lengths, depending on the printer paper path requirements, and typically has driving or supporting rollers 24A, 24B supporting opposite ends of the belts 22. All of the preceding is well-known to those skilled in the art and need not be described in further detail herein.

[0019] In this improved system 10, what would normally be an open exhaust for the vacuum blower 30 is instead connected to a closed positive air pressure conducting or manifold system connecting to a positive air pressure plenum 32. The plenum 32 extends transversely across the sheet feed path overlying the vacuum belt sheet transport system 16 with downwardly opening slits 32A providing downwardly projecting air jets acting against the top of the sheet 14 curled up forward edge area coming out of the fuser 12 nip, thereby pushing the forward edge of the sheet 14 down against the vacuum sheet transport system 16 in cooperation with the airflow from the vacuum in the negative pressure manifold 20 under the belts 22, thereby enabling the relatively planar transport of the sheet 14 along the generally planar top surface of the belts 22 with good acquisition and with reduced danger of a rapidly moving sheet 14 “airplaning” away from the belts 22.

[0020] The slots 32A (slots or holes) in the positive pressure plenum 32 providing downward air jets in the disclosed embodiment may be sized to provide sufficient velocity to their issuing airflow such that the stagnation pressure generated from the jet impingement is substantially larger than the lift forces created by the beam strength of the curled sheet and the pneumatic lift or airplaning forces from the forward movement of even a curl sheet moving at relatively high process speed. For example, a plurality of only about 0.6 cm wide slots 32A extending transversely across the sheet feed path at a flow rate of only about 0.5 cubic meters per second was found to be sufficient in one test fixture.

[0021] It will be appreciated that various presently unforeseen or unanticipated alternatives, modifications, variations or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims. 

What is claimed is:
 1. In a sheet transport system with a sheet feeding path for transporting flimsy print media sheets having upper and lower surfaces, at lease some of which flimsy print media sheets in said sheet transport system are curled, said sheet transport system including at least one vacuum sheet transport system and at least one non-vacuum sheet transport system; wherein said vacuum sheet transport system has a vacuum blower providing a vacuum airflow to said vacuum sheet transport system for providing vacuum attraction of the lower surface of said sheets against said vacuum sheet transport system, and wherein said vacuum blower has a positive air pressure exhaust airflow output corresponding to said vacuum airflow; wherein a positive air pressure airflow system is provided and positioned to direct positive pressure air flow against at least a portion of the upper surface of said flimsy print media sheets being fed in said sheet transport system to blow said curled towards said sheet feeding path.
 2. The sheet transport system of claim 1, wherein said positive air pressure airflow system providing a positive air pressure against said flimsy print media sheets is provided by said exhaust airflow output of said vacuum blower.
 3. The sheet transport system of claim 1, wherein said non-vacuum sheet transport system is a fuser imparting curl to at least some of said flimsy print media sheets, which curled print media sheets are being fed towards said vacuum sheet transport system, and wherein said positive air pressure airflow system providing a positive air pressure against said flimsy print media sheets is blowing said sheets towards said vacuum sheet transport system to assist in the engagement of said curled print media sheets by said vacuum sheet transport system.
 4. The sheet transport system of claim 1, wherein said positive air pressure airflow system includes a positive air pressure manifold extending transversely over at least one end of said vacuum sheet transport system, spaced therefrom and feeding positive air pressure air to one or more air jets providing positive pressure air flow towards at least the leading edge area of said flimsy print media sheets being fed onto said vacuum sheet transport system.
 5. In a sheet transport system with a sheet feeding path for transporting flimsy print media sheets having a tendency for curled sheet edges downstream in said sheet feeding path, said sheet transport system including a downstream pneumatic vacuum sheet transport system and an upstream non-vacuum sheet transport system feeding said curled edge sheets onto said downstream pneumatic vacuum sheet transport system; wherein said downstream pneumatic vacuum sheet transport system has a pneumatic vacuum source with a vacuum airflow input to said downstream pneumatic vacuum sheet transport system for providing vacuum attraction of said sheets against said downstream pneumatic vacuum sheet transport system, and wherein said pneumatic vacuum source has a positive air pressure exhaust airflow output system corresponding to said vacuum airflow input, and wherein said positive air pressure exhaust airflow output system is positioned to direct positive pressure air flow towards at least the upstream edge of said downstream pneumatic vacuum sheet transport system and towards a curled sheet edge being fed onto said downstream pneumatic vacuum sheet transport system by said upstream non-vacuum sheet transport system, to blow said curled sheet edge towards vacuum engagement with said downstream pneumatic vacuum sheet transport system.
 6. The sheet transport system of claim 5, wherein said upstream non-vacuum sheet transport system is a xerographic thermal roll fuser imparting curl to said flimsy print media sheets.
 7. A method of transporting flimsy print media sheets having curled sheet edges comprising feeding said curled sheets out over a vacuum sheet transport belt system and attracting the sheet there towards with an underlying vacuum manifold airflow and simultaneously blowing the upper surface of the sheet down towards said vacuum belt transport with a positive pressure airflow, wherein both said vacuum manifold airflow and said positive pressure airflow applied to the upper surface of the sheet are respectively provided solely by the air intake and the air exhaust from a single air blower.
 8. The method of transporting flimsy print media sheets having curled sheet edges of claim 7, wherein said positive pressure airflow is provided from a positive air pressure manifold extending transversely over at least the upstream end of said vacuum sheet transport belt system, spaced therefrom, which positive air pressure manifold is feeding air to one or more air jets providing said positive pressure air flow towards at least the curled sheet edge being fed out over said vacuum sheet transport belt system. 